Nonaqueous secondary battery

Abstract: A nonaqueous secondary battery comprising a positive electrode active material, a negative electrode active material, and a lithium salt is disclosed, in which the negative electrode active material contains (1) a compound capable of intercalating and deintercalating lithium comprising an atom of the group IIIB, IVB or VB of the periodic table, (2) an amorphous compound containing at least two atoms selected from the elements of the groups IIIB, IVB, and VB of the periodic table, (3) a compound capable of intercalating and deintercalating lithium containing at least one of the atoms of the group IIIB, IVB, and VB of the periodic table and fluorine, or (4) a compound of the metal of the group IIIB, IVB or VB of the periodic table, Zn, or Mg which is capable of intercalating and deintercalating lithium. The nonaqueous secondary battery of the invention exhibits improved charge and discharge characteristics and improved safety.

Description: FIELD OF THE INVENTION This invention relates to a nonaqueous secondary battery having improved charge and discharge cycle characteristics and improved safety. BACKGROUND OF THE INVENTION Negative electrode active materials for nonaqueous secondary batteries typically include metallic lithium and lithium alloys. The problem associated with these active materials is that metallic lithium grows dendritically during charging and discharging to cause an internal short circuit, involving a danger of ignition because of high activity of the dendritical metal per se . To solve the problem, a calcined carbonaceous material capable of intercalating and deintercalating lithium has recently been put to practical use. However, since the carbonaceous material has electrical conductivity by itself, metallic lithium is sometimes precipitated on the carbonaceous material at the time of an overcharge or a rapid charge. It eventually follows that lithium grows dendritically thereon. This problem has been dealt with by altering a charger or reducing the amount of the positive electrode active material to prevent an overcharge. Where the latter solution is adopted, however, the limited amount of the active material leads to a limited discharge capacity. Further, the carbonaceous material has a relatively low density and therefore a low capacity per unit volume. Thus, the discharge capacity is limited by both the amount of the active material and the capacity per unit volume. In addition to metallic lithium, lithium alloys and the above-mentioned carbonaceous material, negative electrode active materials so far proposed include TiS 2 and LiTiS 2 which are capable of intercalating and deintercalating lithium (U.S. Patent 3,983,476); transition metal oxides having a rutile structure, such as WO 2 (U.S. Patent 4,198,476), spinel compounds, such as Li x Fe(Fe 2 )O 4 (JP-A-58-220362, the term "JP-A" as used herein means an "unexamined published Japanese patent application"); a electrochemically synthesized lithium compound of Fe 2 O 3 (U.S. Patent 4,464,447); a lithium compound of Fe 2 O 3 (JP-A-3-112070); Nb 2 O 5 (JP-B-62-59412 (the term "JP-B" as used herein means an "examined published Japanese patent application") and JP-A-2-82447); FeO, Fe 2 O 3 , Fe 3 O 4 , CoO, Co 2 O 3 , and Co 3 O 4 (JP-A-3-291862); amorphous V 2 O 5 (JP-A-4-223061); and transition metal oxides having their basic crystal structure changed by intercalation of a lithium ion (EP 567149). Any of these known compounds has a high oxidation-reduction potential, failing to provide a nonaqueous secondary battery having a discharge potential as high as 3 V and a high capacity. SnO 2 or Sn compounds are used as an active material of lithium batteries as in Li 1.03 Co 0.95 Sn 0.04 O 2 as a secondary battery positive electrode active material (EP 86-106301); SnO 2 -added V 2 O 5 as a secondary battery positive electrode active material (JP-A-2-158056); SnO 2 -added α-Fe 2 O 3 (preferred SnO 2 content: 0.5 to 10 mol%) as a secondary battery negative electrode active material (JP-A-62-219465); and SnO 2 as a primary battery positive electrode active material (Denki Kagaku oyobi Kogyo Butsuri Kagaku , Vol. 46, No. 7, p. 407 (1978)). With reference to the use of SnO 2 or Sn compounds as an electrochromic electrode, it is known that SnO 2 is capable of reversible intercalation of an Li ion (see Journal of Electrochemical Society , Vol. 140, No. 5, L81 (1993) and that a film comprising InO 2 doped with 8 mol% of Sn (i.e., ITO) is capable of reversible intercalation of an Li ion (see Solid State Ionics, Vols. 28-30, p. 1733 (1988)). However, the electrode useful in an electrochromic system should be transparent, the active material is used in the form of a thin film formed by, for example, vacuum evaporation, and the electrode usually works at a considerably low current differing from the practical range of batteries. For example, Solid State Ionics , supra , shows a working current of 1 µA to 30 µA/cm 2 as an experimental example. Known positive electrode active materials include spinel compounds disclosed in JP-B-4-30146 and cobalt oxide disclosed in JP-B-63-59507. It is possible to combine these positive electrode active materials with an oxide mainly comprising Sn as a negative electrode active material to provide a nonaqueous secondary battery having a high discharge potential, a high capacity, improved charge and discharge cycle characteristics, and increased safety. Yet, the charge and discharge cycle characteristics are still unsatisfactory as described above, and it has been keenly demanded to further improve charge and discharge cycle characteristics. SUMMARY OF THE INVENTION An object of the present invention is to provide a nonaqueous secondary battery having improved charge and discharge cycle characteristics, a high discharge potential, a high discharge capacity, and increased safety. The above object of the present invention is accomplished by a nonaqueous secondary battery comprising a positive electrode active material, a negative electrode active material, and a lithium salt, in which the negative electrode active material is a compound capable of intercalating and deintercalating lithium containing at least one of the atoms of the group IIIB, IVB, and VB of the periodic table and fluorine. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is the X-ray diffraction pattern of compound SnSiO 3 . Fig. 2 is a cross section of a coin battery prepared in Examples, wherein 1 indicates a negative electrode sealing plate, 2 indicates a negative electrode active material mixture pellet, 3 indicates a separator, 4 indicates a positive electrode active material mixture pellet, 5 indicates a collector, 6 indicates a positive electrode case, and 7 indicates a gasket. Fig. 3 is a cross section of a cylindrical battery prepared in Examples, wherein 8 indicates a positive electrode sheet, 9 indicates a negative electrode sheet, 10 indicates a separator, 11 indicates a battery case, 12 indicates a battery cover, 13 indicates a gasket, and 14 indicates a safety valve. DETAILED DESCRIPTION OF THE INVENTION The terminology "negative electrode active material precursor" as used herein is explained below. The inventors have found that SnO having an α-PbO structure, SnO 2 having a rutile structure, and the like do not act by themselves as a negative electrode active material of a secondary battery but change their crystal structure on intercalation of lithium to act as a reversible negative electrode active material. That is, the charge and discharge efficiency of the first cycle is as low as about 80% or 60%. Thus, the starting material, such as α-PbO-structure SnO or rutile-structure SnO 2 , namely, a compound before lithium intercalation is called a "negative electrode active material precursor". The negative electrode active material according to the present invention can be obtained by electrochemically intercalating a lithium ion into, for example, an oxide, an active material precursor. Lithium ion intercalation is conducted until the basic structure of the oxide is changed (for example, until the X-ray diffraction pattern changes) and also until the thus changed basic structure of the Li ion-containing oxide undergoes substantially no change during charging and discharging (for example, the X-ray diffraction pattern does not change substantially). The change in basic structure means change from a certain crystal structure to a different crystal structure or from a crystal structure to an amorphous structure. Where the compound of the present invention described in later is used as a negative electrode active material precursor, it was found that intercalation of lithium does not cause reduction of the respective metal (an alloy with lithium). This can be confirmed from the fact that (1) observation under a transmission electron microscope reveals no precipitation of a metal (especially no precipitation of a dendrite), (2) the potential of lithium intercalation/deintercalation via a metal is different from that of the oxide, and (3) the lithium deintercalation loss with respect to lithium intercalation in SnO was about 1 equivalent, which does not agree with a loss of 2 equivalents in the case where metallic tin is generated. Since the potential of an oxide is similar to that of a currently employed calcined carbonaceous compound, it is assumed that the bonding state of lithium is neither mere ionic bonding nor mere metallic bonding, similarly to a calcined carbonaceous compound. Accordingly, the negative electrode active material of the present invention is obviously different from conventional lithium alloys. It is preferable that the active material precursor which can be used in the present invention is substantially amorphous at the time of battery assembly (before lithium ion intercalation). The term "substantially amorphous" as used herein means that an X-ray diffraction pattern using CuKα rays shows a broad scattering band with peaks between 20° and 40° in terms of 2 and may contain diffraction assigned to a crystalline structure. The maximum intensity of the peaks assigned to the crystalline structure appearing between 2=40° and 70° is preferably not higher than 500 times, still preferably not higher than 100 times, still more preferably not higher than 5 times, the intensity of the peak of the broad scattering band appearing between 2=20° and 40°. It is the most preferred that the pattern exhibits no crystalline diffraction spectrum. According to one of the embodiments of the present invention in which the negative electrode active material is an oxide containing fluorine, the fluorine in the negative electrode active material strengthens the structure and chemical stability of a compound oxide. In particular, fluorine in an amorphous oxide is effective to further enhance the amorphous properties thereby improving the electrochemical structural stability. Specific examples of the fluorine-containing negative electrode active material or a precursor thereof are GeF 0.2 O 0.9 , GeF 0.2 O 1.9 , SnF 0.2 O 0.9 , SnF 0.2 O 1.9 , SnSiF 0.4 O 2.8 , PbF 0.4 O 1.8 , PbF 0.2 O 1.9 , Pb 2 F 0.2 O 2.9 , Pb 3 F 0.4 O 3.8 , Sb 2 F 0.2 O 2.9 , Sb 2 F 0.2 O 3.9 , Sb 2 F 0.2 O 4.9 , Bi 2 F 0.4 O 3.8 , Bi 2 F 0.4 O 3.8 , and Bi 2 F 0.2 O 4.9 , and non-stoichiometrical compounds or compound oxides thereof. Preferred of these fluorine-containing negative electrode active materials are fluorine-containing SnO, SnO 2 , GeO, GeO 2 , and SnSiO 3 , with fluorine-containing SnSiO 3 being still preferred. Fluorine-containing and amorphous SnO, SnO 2 , GeO, GeO 2 , and SnSiO 3 are particularly preferred. A preferred fluorine content in the fluorine-containing negative electrode active material is from 10 to 100 mol%, particularly 20 to 50 mol%, based on the total amount of the metal elements in the active material. The F-containing negative electrode active materials preferably include those represented by formula Sn x SiF y O z (0.2 < x ≤ 1.0; 0 < y ≤ 2; 2.2 < z ≤ 3). The F-containing compound oxide may be crystalline or amorphous but is preferably amorphous. The F-containing negative electrode active material precursor mainly comprising Sn can be synthesized by calcining a mixture of the above-mentioned tin oxide and fluorine compound in air or an inert gas at a high temperature. In the case of adding another metal or metals, a mixture of the tin compound, the fluorine compound, and an oxide of another metal or metals is calcined. For example, fluorine-containing SnSiO 3 can be synthesized by calcining a mixture of SnO, SnF 2 , and SiO 2 in an inert gas at 200° to 1200°C, preferably 500° to 1100°C. For obtaining an amorphous (glassy) active material, the calcined product is quenched at a cooling rate of 1.5° to 100°C/min, preferably 5° to 20°C/min. The fluorine-containing negative electrode active material precursor can also be synthesized by co-precipitation in a solution (co-precipitation method). In this case, an acidic or alkaline aqueous solution containing, for example a salt of the group IIIB, IVB, or VB element is neutralized in the presence of a fluoride ion to form a fluorine-containing compound hydroxide or a fluorine-containing compound oxide. The negative electrode active material precursors containing other metals can also be synthesized by the above-described calcination method or co-precipitation method. The positive electrode active material which can be used in the present invention may be a transition metal oxide capable of reversibly intercalating and deintercalating a lithium ion but is preferably a lithium-containing transition metal oxide. Lithium-containing transition metal oxides which can be used as a positive electrode active material include, for preference, lithium-containing oxides of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo or W. The oxide may contain other alkali metals (the group IA and IIA elements) in addition to Li and/or other elements such as Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, etc. The ratio of these additional elements is preferably up to 30 mol%, still preferably up to 10 mol%, based on the transition metal. Preferred of the Li-containing transition metal oxides as a positive electrode active material are those prepared from a mixture of a lithium compound and at least one compound of a transition metal selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo, and W at a lithium compound/total transition metal compounds molar ratio of 0.3 to 2.2. Still preferred are those prepared from a mixture of a lithium compound and at least one compound of a transition metal selected from V, Cr, Mn, Fe, Co, and Ni at a lithium compound/total transition metal compounds molar ratio of from 0.3 to 2.2. The most preferred are those represented by formula Li x QO y (Q represents at least one transition metal selected from Co, Mn, Ni, V, and Fe; x is from 0.2 to 1.2; and y is from 1.4 to 3). Q may contain, in addition to a transition metal, other metals, such as Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, etc. The ratio of the other metals is preferably up to 30 mol% based on the total transition metals. Suitable examples of the lithium-containing metal oxide positive electrode active material which can be preferably used in the present invention are Li x CoO 2 , Li x NiO 2 , Li x MnO 2 , Li x Co a Ni 1-a O 2 , Li x Co b V 1-b O 2 , Li x Co b Fe 1-b O 2 , Li x Mn 2 O 4 , Li x Mn c Co 2-c O 4 , Li x Mn c Ni 2-c O 4 , Li x Mn c V 2-c O z , Li x Mn c Fe 2-c O 4 , a mixture of Li x Mn 2 O 4 and MnO 2 , a mixture of Li 2x MnO 3 and MnO 2 , a mixture of Li x Mn 2 O 4 , Li 2x MnO 3 , and MnO 2 (wherein x = 0.2 to 1.2; a = 0.1 to 0.9; b = 0.8 to 0.98; c = 1.6 to 1.96; and z = 2.01 to 5). Preferred examples of the lithium-containing metal oxide positive electrode active materials are Li x CoO 2 , Li x NiO 2 , Li x MnO 2 , Li x Co a Ni 1-a O 2 , Li x Co b V 1-b O z , Li x Co b Fe 1-b O 2 , Li x Mn 2 O 4 , Li x Mn c Co 2-c O 4 , Li x Mn c Ni 2-c O 4 , Li x Mn c V 2-c O 4 , and Li x Mn c F 2-c O 4 (wherein x = 0.7 to 1.2; a = 0.1 to 0.9; b = 0.8 to 0.98; c = 1.6 to 1.96; z = 2.01 to 2.3). Still preferred of the lithium-containing metal oxide positive electrode active materials are Li x CoO 2 , Li x NiO 2 , Li x MnO 2 , Li x Co a Ni 1-a O 2 , Li x Mn 2 O 4 , and Li x Co b V 1-b O z (wherein x = 0.7 to 1.2; a = 0.1 to 0.9; b = 0.9 to 0.98; and z = 2.01 to 2.3). The most preferred are Li x CoO 2 , Li x NiO 2 , Li x MnO 2 , Li x Co a Ni 1-a O 2 , Li x Mn 2 O 4 , and Li x Co b V 1-b O z (wherein x = 0.7 to 1.2; a = 0.1 to 0.9; b = 0.9 to 0.98; and z = 2.02 to 2.3). The value x in the above formulae is the value before commencement of charging and discharging and varies with a charge and a discharge. According to another embodiment of the present invention, a spinel type manganese-containing oxide is used as a positive electrode active material. Spinel type oxides have a spinel structure represented by formula A(B 2 )O 4 , in which the oxygen anions are aligned in cubic closest packing and occupy part of the faces and apexes of a tetrahedron and an octahedron. The unit cell is composed of 8 molecules, and oxygen occupies 32e positions in the Fd3m space. The unit cells occupy the lattice spacing of 64 octahedrons at three crystallographically non-equivalent positions, 8a, 8b, and 48f. In this spinel structure, cations B are positioned at the lattice spacing sites of the 16d octahedrons (the vacant octahedron site is 16c), and cations A are positioned at the lattice spacing sites of the 8a tetrahedrons. Each 8a octahedron shares the face with the adjoining 4 vacant 16c octahedrons thereby to provide passageways through which cations A diffuse (e.g., 8a → 16c → 8a → 16c). On the other hand, each 8b tetrahedron shares the face with the 16d octahedron formed of cations B, resulting in energy disadvantage to cations' occupation. The 48f tetrahedron shares the face with both the 16d and 16c octahedrons. According to the distribution of cations A, A(B 2 )O 4 is called a normal spinel structure, and B(AB)O 4 is called an inverse-spinel structure. A x B y (A 1-x B 1-y )O 4 , an intermediate structure between a normal spinel and an inverse-spinel, is also called a spinel. Manganese oxides having a normal spinel structure typically include LiMn 2 O 4 , which serves as a positive electrode active material. In this structure, a half of the Mn cations are trivalent, with the another half being tetravalent. λ-MnO 2 , also known as an active material, is regarded to have a spinel structure with defects, derived by removing lithium from LiMn 2 O 4 , in which all the Mn cations are tetravalent, as described in U.S. Patent 4,246,253. The manganese oxide positive electrode active materials which can be used in the present invention include all of those having a normal spinel structure, those having an inverse-spinel structure, those having a defect-free structure, and those having a non-stoichiometrical spinel structure with defects. Suitable Li-containing manganese oxides having a spinel structure which can be used in the present invention include those represented by general formula Li 1+x [Mn 2-y ]O 4 (0 < x < 1.7; 0 ≤ y < 0.7). Such compounds include Li 4 Mn 5 O 12 (or Li[Li 1/3 Mn 5/3 ]O 4 ). In addition, the following compounds are also included under the scope covered by the above general formula (structural formulae include those represented by multiplying the general formula by an integer or a decimal): Li 4 Mn 4 O 9 , LiMnO 2 (or Li 2 Mn 2 O 4 ), Li 2 MnO 3 , Li 5 Mn 4 O 9 , and Li 4 Mn 5 O 12 Suitable Li-containing manganese oxides having a spinel structure which can be used as a positive electrode active material in the present invention further include those represented by general formula Li 1-x [Mn 2-y ]O 4 (0 < x < 1.0; 0 ≤ y < 0.5). Preferred of them are those represented by general formula Li 1-x [Mn 2-y ]O 4 (0.20 < x < 1.0; 0 < y < 0.2), such as Li 2 Mn 5 O 11 (or Li 1-x [Mn 2-y ]O 4 (x = 0.273; y = 0.182)), which is a non-stoichiometrical spinel compound disclosed in JP-A-4-240117; and those represented by general formula Li 1-x [Mn 2-y ]O 4 (0 < x ≤ 0.20; 0 < y < 0.4), such as Li 2 Mn 4 O 9 . In addition, the following compounds are also included under the scope covered by the above formula Li 1-x [Mn 2-y ]O 4 (structural formulae include those represented by multiplying the general formula by an integer or a decimal): Li 4 Mn 16.5 O 35 , Li 2 Mn 7.5 O 16 , and Li 0.7 MnO 4 The above-mentioned spinel type manganese oxides as a positive electrode active material can be obtained by reacting a lithium salt and a manganese salt or a manganese oxide in a solid phase at a high temperature according to a known method. In using lithium carbonate and manganese dioxide as starting materials, calcination is carried out at 350° to 900°C, preferably 350° to 500°C, for 8 to 48 hours. In using lithium nitrate having a low melting point (261°C) as a lithium salt, calcination is carried out at 300° to 900°C, preferably 300° to 500°C. Manganese oxides to be used include λ-MnO 2 , electrolytically prepared MnO 2 (EMD), chemically prepared MnO 2 (CMD), and a mixture thereof. Lithium-manganese double oxides (e.g., Li 2 Mn 4 O 9 ) may also be used as a lithium material. In this case, the Li-Mn double oxide is mixed with a manganese material, e.g., manganese dioxide, and calcined at 350° to 500°C. The spinel type manganese oxide may be doped with one or more of other transition metal elements, typical elements, and rare earth elements to form a compound oxide. Preferred dopants are transition metal elements, such as Co, Ni, Ti, V, Zr, Nb, Mo, W, and Fe. The positive electrode active materials which can be used in the present invention also include manganese oxide compounds having a hollandite skeleton structure as disclosed in JP-A-4-270125, which are regarded as having the above-described general formulae with part or most part (e.g., 95% or more) of Li cations thereof being substituted with other cations, e.g., H, K, Na, and ammonium ions. Hollandite type compounds in which Li cations are substituted with H can easily be obtained by, for example, treating an Li-Mg double oxide represented by the above general formula with an acid at a high temperature to remove Li. The positive electrode active materials can be synthesized by mixing a lithium compound and a transition metal compound, followed by calcination or by reacting these materials in a solution. The former calcination method is preferred. Calcination is carried out at a calcination temperature selected from the range in which at least part of the mixed compounds may be decomposed and melted, for example, from 250° to 2000°C, preferably from 350° to 1500°C, for 1 to 72 hours, preferably 2 to 20 hours. Prior to calcination, the mixture is preferably pre-calcined at 250° to 900°C. Mixing of the raw materials may be either dry blending or wet blending. If desired, calcination may be followed by annealing at 200° to 900°C. The calcination atmosphere is not limited and may be an oxidizing atmosphere or a reducing atmosphere. For example, calcination can be performed in air, a prepared gas having an arbitrary oxygen concentration, hydrogen, carbon monoxide, nitrogen, argon, helium, krypton, xenon, or carbon dioxide. In the synthesis of positive electrode active materials, chemical intercalation of a lithium ion into a transition metal oxide is preferably achieved by reacting metallic lithium, a lithium alloy or butyl lithium with the transition metal oxide. While not limiting, the positive electrode active material to be used in the present invention preferably has an average particle size of from 0.1 to 50 µm and a BET specific surface area of from 0.01 to 50 m 2 /g. An aqueous solution (supernatant liquid) of 5 g of a positive electrode active material in 100 ml of distilled water preferably has a pH of 7 to 12. The resulting positive electrode active material can be ground to size by means of well-known grinding machines or classifiers, such as a mortar, a ball mill, a vibration ball mill, a vibration mill, a satellite ball mill, a planetary ball mill, a spinning air flow type jet mill, and a sieve. If desired, the positive electrode active material obtained by calcination may be washed with water, an aqueous acid solution, an aqueous alkali solution or an organic solvent before use. Lithium is intercalated into a compound according to the invention in an amount of from 1 to 20 equivalents, preferably from 3 to 10 equivalents. The ratio of a positive electrode active material to a negative electrode active material is decided according to the above-mentioned equivalent amount. It is preferable to use a positive electrode active material in an amount based on the calculated ratio multiplied by 0.5 to 2. Where any other substance than a positive electrode active material, e.g., metallic lithium, a lithium alloy or butyl lithium, is used as a lithium source, the amount of a positive electrode active material to be used is decided in conformity with the equivalent amount of deintercalated lithium of the negative electrode active material. In this case, too, the ratio based on the equivalent amount is preferably multiplied by 0.5 to 2. Negative electrode active materials which may be used in combination with the negative electrode active material of the present invention include metallic lithium, lithium alloys (e.g., alloys with Al, Al-Mn, Al-Mg, Al-Sn, Al-In or Al-Cd), and calcined carbonaceous compounds capable of intercalating and deintercalating a lithium ion or metallic lithium. An electrode material mixture which can be used in the present invention comprises the above-described active material, a conducting agent, a binder, a filler, and so forth. The conducting agent may be any electron-conducting material which undergoes no chemical change in an assembled battery. Suitable conducting agents include natural graphite (scale graphite, flake graphite, lumpy graphite, etc.), artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powders (e.g., copper, nickel, aluminum or silver powder), metallic fibers, polyphenylene derivatives, and mixtures of two or more thereof. A combination of graphite and acetylene black is particularly preferred. The conducting agent is preferably used in an amount of from 1 to 50% by weight, still preferably from 2 to 30% by weight, based on the total weight of the active material mixture. Carbon or graphite is preferably used in an amount of from 2 to 15% by weight. The binder includes polysaccharides, thermoplastic resins, and rubbery polymers; such as starch, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl pyrrolidone, tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene-propylene-diene terpolymers (EPDM), sulfonated EPDM, styrene-butadiene rubbers, polybutadiene, fluorine rubbers, polyethylene oxide, and mixtures of two or more thereof. In using a compound having a functional group reactive with lithium, such as a polysaccharide, it is preferable to deactivate the functional group by addition of a compound having an isocyanate group. The binder is used in an amount of 1 to 50% by weight, preferably 2 to 30% by weight, based on the total weight of the active material mixture. In particular, polymers having a decomposition temperature of not lower than 300°C are preferred as a binder for the negative electrode active material of the present invention. Such polymers include polyethylene, polypropylene, epoxy resins, polyester resins, and fluorine resins, with fluorine resins being preferred. The term "fluorine resin" is used herein as a general term for polymers having a carbon-fluorine bond in the molecule thereof as specified in JIS K6900 "Glossary of Terms Used in Plastic Industry". Suitable examples of the fluorine resins are shown below. (A-1) Polytetrafluoroethylene (PTFE) (A-2) Polyvinylidene fluoride (PVDF) (A-3) Tetrafluoroethylene-hexafluoropropylene copolymer (FEP) (A-4) Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) (A-5) Vinylidene fluoride-hexafluoropropylene copolymer (A-6) Vinylidene fluoride-chlorotrifluoroethylene copolymer (A-7) Ethylene-tetrafluoroethylene copolymer (ETFE resin) (A-8) Polychlorotrifluoroethylene (PCTFE) (A-9) Vinylidene fluoride-pentafluoropropylene copolymer (A-10) Propylene-tetrafluoroethylene copolymer (A-11) Ethylene-chlorotrifluoroethylene copolymer (ECTFE) (A-12) Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (A-13) Vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer Copolymer resins comprising another ethylenically unsaturated monomer in addition to the above-mentioned monomers are also useful. Specific but non-limiting examples of copolymerizable unsaturated monomers include acrylic esters, methacrylic esters, vinyl acetate, acrylonitrile, acrylic acid, methacrylic acid, maleic anhydride, butadiene, styrene, N-vinylpyrrolidone, N-vinylpyridine, glycidyl methacrylate, hydroxyethyl methacrylate, and methyl vinyl ether. The binder resins can be obtained by any of solution polymerization, emulsion polymerization, suspension polymerization, and gaseous phase polymerization, and the polymer may be any of random polymers, graft polymers, and block polymers. The above-mentioned binder resin may be used in combination with one or more other polymers, such as carboxymethyl cellulose, sodium polyacrylate, hydroxyethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, and alginic acid. The binder is preferably used in an amount of from 0.5 to 30% by weight based on the negative electrode active material. The filler to be used in the present invention is not particularly limited as long as it is a fibrous material undergoing no chemical change in an assembled battery. Suitable fillers include fibers of polyolefins (e.g., polypropylene or polyethylene), glass fiber, and carbon fiber. While not limiting, the filler is preferably used in an amount of up to 30% by weight based on the total weight of the active material mixture. The nonaqueous electrolytic solution which can be used in the nonaqueous secondary battery of the present invention consists of at least one organic solvent and at least one lithium salt soluble in the solvent. Suitable organic solvents include aprotic solvents, such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, methyl propionate, ethyl propionate, phosphoric triesters, trimethoxymethane, dioxolane derivatives, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, and 1,3-propanesultone. These solvents may be used either individually or in combination of two or more thereof. Suitable lithium salts soluble in these solvents include LiClO 4 , LiBF 6 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiB 10 Cl 10 , lower aliphatic lithium carboxylates, LiAlCl 4 , LiCl, LiBr, LiI, chloroboran lithium, and lithium tetraphenylborate. These lithium salts may be used either individually or in combination of two or more thereof. In particular, a solution of LiCF 3 SO 3 , LiClO 4 , LiBF 4 and/or LiPF 6 in a mixed solvent of propylene carbonate or ethylene carbonate and 1,2-dimethoxyethane and/or diethyl carbonate is a preferred electrolytic solution. The amount of the electrolytic solution to be used in a battery is not particularly limited and can be selected according to the amounts of the positive and negative electrode active materials or the size of the battery. The concentration of the supporting electrolyte is preferably from 0.2 to 3 mols per liter of the electrolytic solution. In addition to electrolytic solutions, inorganic or organic solid electrolytes may also be employed. Examples of suitable inorganic solid electrolytes include a lithium nitride, a lithium halide, and a lithium oxyacid salt. Among them preferred are Li 3 N, LiI, Li 5 NI 2 , Li 3 N-LiI-LiOH, LiSiO 4 , LiSiO 4 -LiI-LiOH, xLi 3 PO 4 -(1-x)Li 4 SiO 4 , Li 2 SiS 3 , and phosphorus sulfide compounds. Examples of suitable organic solid electrolytes include polyethylene oxide derivatives or polymers containing the same (see JP-A-63-135447), polypropylene oxide derivatives or polymers containing the same, polymers containing an ionizing group (see JP-A-62-254302, JP-A-62-254303, and JP-A-63-193954), a mixture of a polymer containing an ionizing group and the above-mentioned aprotic electrolytic solution (see U.S. Patents 4,792,504 and 4,830,939, JP-A-62-22375, JP-A-62-22376, JP-A-63-22375, JP-A-63-22776, and JP-A-1-95117), and phosphoric ester polymers (see JP-A-61-256573). A combination of polyacrylonitrile and an electrolytic solution (see JP-A-62-278774) and a combination of an organic solid electrolyte and an inorganic solid electrolyte (see JP-A-60-1768) are also known. As a separator, an insulating thin film having high ion permeability and prescribed mechanical strength is used. A sheet or nonwoven fabric made of an olefin polymer (e.g., polypropylene), glass fiber or polyethylene is usually employed for their organic solvent resistance and hydrophobic properties. The pore size of the separator is selected from the range generally used for batteries, e.g., from 0.01 to 10 µm. The thickness of the separator is selected from the range generally used for batteries, e.g., from 5 to 300 µm. For the purpose of improving charge and discharge characteristics, the electrolytic solution may contain other compounds, such as pyridine (see JP-A-49-108525), triethyl phosphite (see JP-A-47-4376), triethanolamine (see JP-A-52-72425), a cyclic ether (see JP-A-57-152684), ethylenediamine (see JP-A-58-87777), n-glyme (see JP-A-58-87778), hexaphosphoric acid triamide (see JP-A-58-87779), a nitrobenzene derivative (see JP-A-58-214281), sulfur (see JP-A-59-8280), a quinoneimine dye (see JP-A-59-68184), an N-substituted oxazolidinone and an N,N'-substituted imidazolidinone (see JP-A-59-154778), an ethylene glycol dialkyl ether (see JP-A-59-205167), a quaternary ammonium salt (see JP-A-60-30065), polyethylene glycol (see JP-A-60-41773), pyrrole (see JP-A-60-79677), 2-methoxyethanol (see JP-A-60-89075), AℓCℓ 3 (see JP-A-61-88466), a monomer providing a conductive polymeric active material (see JP-A-61-161673), triethylenephosphoramide (see JP-A-61-208758), a trialkylphosphine (JP-A-62-80976), morpholine (see JP-A-62-80977), an aryl compound having a carbonyl group (see JP-A-62-86673), hexamethylphosphoric triamide and a 4-alkylmorpholine (see JP-A-62-217575), a bicyclic tertiary amine (see JP-A-62-217578), an oil (see JP-A-62-287580), a quaternary phosphonium salt (see JP-A-63-121268), and a tertiary sulfonium salt (see JP-A-63-121269). In order to make the electrolytic solution incombustible, a halogen-containing solvent, such as carbon tetrachloride or trifluorochloroethylene, may be added to the electrolytic solution (see JP-A-48-36632). In order to make the electrolytic solution resistant to high-temperature preservation, carbonic acid gas may be incorporated thereto (see JP-A-59-134567). The positive or negative electrode active material mixture may contain an electrolytic solution or an electrolyte. For example, it is known to add the above-mentioned ion-conductive polymer or nitromethane (see JP-A-48-36633) or an electrolytic solution (see JP-A-57-12487) to the active material mixture. The surface of the positive electrode active material may be modified by treating with an esterification agent (see JP-A-55-163779), a chelating agent (see JP-A-55-163780), a conducting high polymer (see JP-A-58-163188 and JP-A-59-14274), polyethylene oxide (see JP-A-60-97561), and the like. The surface of the negative electrode active material may also be modified by, for example, providing a layer comprising an ion-conductive polymer or polyacetylene (see JP-A-58-111276) or treating with LiCℓ (see JP-A-58-142771). A collector for an active material may be made of any electron-conducting substance which undergoes no chemical change in an assembled battery. Suitable materials of a collector for the positive electrode include stainless steel, nickel, aluminum, titanium, calcined carbon; and aluminum or stainless steel with its surface treated with carbon, nickel, titanium or silver. Suitable materials of a collector for the negative electrode include stainless steel, nickel, copper, titanium, aluminum, calcined carbon; copper or stainless steel with its surface treated with carbon, nickel, titanium or silver; and an Aℓ-Cd alloy. These materials may be subjected to surface oxidation. The collector may have a variety of forms, such as a foil, a film, a sheet, a net, a punched sheet, a lath, a porous body, a foamed body, a fibrous body, and so on. While not limiting, the thickness of the collector is from 1 to 500 µm. The battery according to the present invention may have any shape, such as a coin shape, a button shape, a sheet shape, a cylindrical shape, and an angular shape. A coin-shaped or button-shaped battery is generally produced by compressing a positive or negative active material mixture into a pellet having prescribed thickness and diameter according to the size of the battery. A sheet, cylindrical or angular battery is generally produced by coating a collector with a positive or negative active material mixture, followed by drying and compressing. The thickness, length or width of the coating layer are decided according to the size of the battery. In particular, the dry thickness (thickness after compression) is preferably selected from the range 1 to 2000 µm. The application of the nonaqueous secondary battery of the present invention is not particularly limited. For example, it is useful in electronic equipment, such as notebook-size color or monochromatic personal computers, pen input personal computers, pocket-size (palmtop) personal computers, notebook-size word processors, pocket-size word processors, electron book players, pocket phones, wireless extentions of key telephone sets, pagers, handy terminals, portable facsimiles, portable copying machines, portable printers, headphone stereos, video cameras, liquid crystal TV sets, handy cleaners, portable CD, mini disk systems, electrical shavers, machine translation systems, land mobile radiotelephones, transceivers, electrical tools, portable calculators, memory cards, tape recorders, radios, backup powers, and so on; automobiles, electrically-powered vehicles, motors, lights, toys, family (home) computers, load conditioners, irons, watches, stroboscopic lamps, cameras, medical equipment (e.g., pacemakers, hearing aids, and massaging machines); military equipment; and spacecraft equipment. The nonaqueous secondary battery of the present invention may be used in combination with solar batteries. The present invention will now be illustrated in greater detail with reference to Examples, but the present invention should not be construed as being limited thereto. All the percents are by weight unless otherwise indicated. SnO, GeO 2 , and PbO 2 used in the following Examples are commercially available ones. SYNTHESIS EXAMPLE E-1 A uniform mixture of SnO and SnF 2 at a molar ratio of 0.9:0.1, totally weighing 20 g, was calcined in an argon atmosphere at 950°C for 6 hours and cooled to room temperature over a period of 2 hours to obtain Snf 0,2 O 0.9 . The calcined product was ground in a grinding machine and sieved to obtain a powdered negative electrode active material precursor having an average particle size of about 10 µm. SYNTHESIS EXAMPLE E-2 A uniform mixture of SnO, SiO 2 , and SnF 2 at a molar ratio of 0.8:1.0:0.2, totally weighing 20 g, was calcined in an argon atmosphere at 1000°C for 6 hours and cooled to room temperature over a period of 2 hours to obtain glassy amorphous SnSiF 0.4 O 2.8 as a yellow solid. The calcined product was ground in a grinding machine and sieved to obtain a powdered negative electrode active material precursor having an average particle size of about 5 µm. Alternatively, a 5% acidic aqueous solution containing SnCl 2 and SiCl 4 at a molar ratio of 0.8:1.0 was neutralized with aqueous ammonia while stirring. The stirring was continued for an additional period of 4 hours while keeping at 80 to 90°C, and the thus formed precipitate was collected by filtration and dried in vacuo at 200°C for 24 hours to obtain Sn 0.8 SiO 2.8 as a yellow powder. The powder was mixed with SnF 2 at a molar ratio of 1:0.2. A 20 g portion of the mixture was heat treated at 1000°C for 1 hour in an argon atmosphere to obtain glassy amorphous SnSiF 0.4 O 2.8 as a yellow solid. SYNTHESIS EXAMPLE E-3 A uniform mixture of SnO, SiO 2 , SnF 2 , and GeO 2 at a molar ratio of 0.8:1.0:0.2:0.1, totally weighing 20 g, was calcined in an argon atmosphere at 1000°C for 6 hours and cooled to room temperature over a period of 2 hours to obtain glassy amorphous SnSiGe 0.1 F 0.4 O 3.0 as a yellow solid. The calcined product was ground in a grinding machine and sieved to obtain a powdered negative electrode active material precursor having an average particle size of about 6 µm. In the same manner as described above but using stoichiometrical amounts of the respective raw materials, SnSiTi 0.1 F 0.4 O 3.0 , SnSiAl 0.1 F 0.4 O 3.0 , SnSiFe 0.1 F 0.4 O 3.0 , and SnSiZn 0.1 F 0.4 O 3.0 were synthesized. SYNTHESIS EXAMPLE E-4 A uniform mixture of SnO, GeO 2 , and SnF 2 at a molar ratio of 0.8:1.0:0.2, totally weighing 20 g, was calcined in an argon atmosphere at 1000°C for 6 hours and cooled to room temperature over a period of 2 hours to obtain glassy amorphous SnGeF 0.4 O 2.8 as a yellow solid. The calcined product was ground in a grinding machine and sieved to obtain a powdered negative electrode active material precursor having an average particle size of about 4 µm. SYNTHESIS EXAMPLE E-5 A uniform mixture of SnO, PbO 2 , and SnF 2 at a molar ratio of 0.8:1.0:0.2, totally weighing 20 g, was calcined in an argon atmosphere at 1000°C for 6 hours and cooled to room temperature over a period of 2 hours to obtain an amorphous solid, SnPbF 0.4 O 2.8 . The calcined product was ground in a grinding machine and sieved to obtain a powdered negative electrode active material precursor having an average particle size of about 8 µm. SYNTHESIS EXAMPLE E-6 A dry mixture of 2.26 g of lithium carbonate, 5.0 g of tricobalt tetroxide, and 0.16 g of zirconium dioxide was calcined in air at 900°C for 18 hours to synthesize crystalline LiCoZr 0.02 O 2 as a positive electrode active material. The resulting product was ground to obtain a brown powder having an average particle size of 5 µm. SYNTHESIS EXAMPLE E-7 A dry mixture of 1.20 g of lithium carbonate and 5.92 g of manganese dioxide was calcined in air at 800°C for 12 hours to synthesize crystalline LiMn 2 O 4 as a positive electrode active material. Average particle size: 3 µm. EXAMPLE E-1 Electrode: A negative electrode active material mixture consisting of 82% of each of the negative electrode active material precursors shown in Table E-1, 8% of flake graphite and 4% of acetylene black as conducting agents, and 6% of polyvinylidene fluoride as a binder was compression molded into a pellet of 13 mm in diameter and 22 mg in weight. For comparative negative electrode active materials, coke (LCP-u, produced by Nippon Steel Chemical Co., Ltd.) and rutile type WO 2 were used. Counter Electrode: A positive electrode active material mixture consisting of 82% of each of the positive electrode active materials shown in Table E-1, 8% of flake graphite, 4% of acetylene black, and 6% of tetrafluoroethylene was compression molded to obtain a pellet of 13 mm in diameter and 110 mg in weight. The negative electrode pellet and the positive electrode pellet were dried in a dry box (dir air; dew point: -40 to -70°C) at 150°C for about 3 hours by means of a far infrared heater. Collector: A 80 µm thick net of SUS316 was welded to each of a positive case and a negative case. Electrolytic Solution: 200 µl of a 1 mol/ℓ solution of LiPF 6 in a 2:2:6 (by volume) mixed solvent of ethylene carbonate, butylene carbonate and dimethyl carbonate. Separator: A finely porous polypropylene sheet and polypropylene nonwoven fabric impregnated with the electrolytic solution. The positive electrode case and the negative electrode case were fitted to each other to prepare a coin lithium battery. The resulting coin battery was subjected to a charge and discharge test under conditions of a constant current density of 0.75 mA/cm 2 , a cut-off voltage of 4.3 V in charging, and a cut-off voltage of 2.7 V in discharging. All the tests were started with lithium intercalation into the negative electrode active material precursor. While more than 50 kinds of coin batteries were prepared and tested using a variety of combinations of a negative electrode active material and a positive electrode active material, only the typical results are shown in Table E-1. It should therefore be understood that the combination of a negative electrode active material and a positive electrode active material which can be used in the present invention is not limited to those shown in Table E-1. Positive Electrode Active Material Negative Electrode Active Material Average Discharge Potential Discharge Capacity at the 2nd Cycle Cycle Characteristics (V) (mAh/g) Comparison: LiCoZr 0.02 O 2 coke 3.40 180 0.10 LiCoZr 0.02 O 2 WO 2 3.20 160 0.15 LiMn 2 O 4 coke 3.30 170 0.12 LiMn 2 O 4 WO 2 3.10 140 0.17 Invention: LiCoZr 0.02 O 2 SnF 0.2 O 0.9 3.53 450 0.07 LiCoZr 0.02 O 2 SnSiF 0.4 O 2.8 3.55 420 0.04 LiCoZr 0.02 O 2 SnSiF 1.0 O 2.5 3.55 410 0.05 LiCoZr 0.02 O 2 SnSiGe 0.1 F 0.4 O 3 3.56 430 0.04 LiCoZr 0.02 O 2 SnSiAl 0.1 F 0.4 O 3 3.56 420 0.03 LiCoZr 0.02 O 2 SnSiTi 0.1 F 0.4 O 3 3.56 420 0.03 LiCoZr 0.02 O 2 SnSiZn 0.1 F 0.4 O 3 3.55 410 0.04 LiCoZr 0.02 O 2 SnSiFe 0.1 F 0.4 O 3 3.54 410 0.05 LiCoZr 0.02 O 3 SnGeF 0.4 O 2.8 3.50 450 0.06 LiCoZr 0.02 O 3 SnPbF 0.4 O 2.8 3.50 400 0.08 LiMn 2 O 4 SnF 0.2 O 0.9 3.50 430 0.08 LiMn 2 O 4 SnSiF 0.4 O 2.8 3.51 400 0.07 LiMn 2 O 4 SnSiGe 0.1 F 0.4 O 3 3.51 400 0.08 LiMn 2 O 4 SnSiAl 0.1 F 0.4 O 3 3.52 410 0.05 LiMn 2 O 4 SnSiTi 0.1 F 0.4 O 3 3.52 400 0.05 LiMn 2 O 4 SnGeF 0.4 O 2.8 3.45 420 0.08 It is obvious from the results in Table E-1 that the nonaqueous secondary batteries using the negative electrode active material according to the present invention are superior in discharge capacity and cycle characteristics to those using conventional negative electrode active materials. According to the present invention, the use of an oxide containing the group IIIB, IVB or VB metal and fluorine furnishes a nonaqueous secondary battery having a high discharge capacity and satisfactory charge and discharge cycle characteristics. Compared with the conventional batteries using coke or WO 2 as a negative electrode active material, the nonaqueous secondary batteries of the present invention have a higher average discharge potential by 0.1 to 0.35 V. Further, the discharge capacity, measured at the 2nd cycle, of the batteries of the present invention is at least double that of the conventional ones. Therefore, the batteries of the present invention are very effective in the applications requiring high power. While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof, which is defined only by the appended claims.

Claims: A nonaqueous secondary battery comprising a positive electrode active material, a negative electrode active material, and a lithium salt, wherein said negative electrode active material is a compound capable of intercalating and deintercalating lithium containing at least one of the atoms of the group IIIB, IVB, and VB of the periodic table and fluorine. A nonaqueous secondary battery as claimed in claim 1, wherein the atom of the group IIIB, IVB and VB of the periodic table is selected from the group consisting of Al, Si, Ge, Sn, Pb, As, and Sb. A nonaqueous secondary battery as claimed in claim 1, wherein said negative electrode active material is a compound which is amorphous at the time of intercalating lithium ion. A nonaqueous secondary battery as claimed in claim 1, wherein said negative electrode active material is a compound which is amorphous at the time of assembling a battery. A nonaqueous secondary battery as claimed in claim 1, wherein said negative electrode active material is obtained by a calcination method consisting of heating at a rate of temperature rise of 4° to 2,000°C/min, maintaining at 250° to 1,500°C for 0.01 to 100 hours, and cooling at a rate of temperature drop of 2° to 10 7 °C/min. A nonaqueous secondary battery as claimed in claim 1, wherein said negative electrode active material is obtained by a calcination method consisting of heating at a rate of temperature rise of 10° to 2,000°C/min, maintaining at 250° to 1,500°C for 0.01 to 100 hours, and cooling at a rate of temperature drop of 2° to 10 7 °C/min. A nonaqueous secondary battery as claimed in claim 1, wherein said positive electrode active material is a lithium-containing transition metal oxide. A nonaqueous secondary battery as claimed in claim 1, wherein said positive electrode active material contains at least one compound represented by formula Li x QO y , wherein Q represents at least one transition metal selected from Co, Mn, Ni, V, and Fe; x is from 0.2 to 1.2; and y is from 1.4 to 3. A nonaqueous secondary battery as claimed in claim 1, wherein said positive electrode active material contains at least one compound selected from Li x CoO 2 , Li x NiO 2 , Li x MnO 2 , Li x Co a Ni 1-a O 2 , Li x Co b V 1-b O z , Li x Co b Fe 1-b O 2 , Li x Mn 2 O 4 , Li x Mn c Co 2-c O 4 , Li x Mn c Ni 2-c O 4 , Li x Mn c V 2-c O 4 , and Li x Mn c Fe e-c O 4 (wherein x = 0.7 to 1.2; a = 0.1 to 0.9; b = 0.8 to 0.98; c = 1.6 to 1.96; z = 2.01 to 2.3). A nonaqueous secondary battery as claimed in claim 1, wherein said positive electrode active material is a lithium-containing manganese compound having a spinel structure and a stoichiometric or non-stoichiometric composition. A nonaqueous secondary battery as claimed in claim 1, wherein lithium is intercalated in an amount of from 1 to 20 equivalents.

Inventors: IDOTA YOSHIO, KUBOTA TADAHIKO, MISHIMA MASAYUKI, MIYAKI YUKIO, MIYASAKA TSUTOMU, IDOTA, YOSHIO, KUBOTA, TADAHIKO, MISHIMA, MASAYUKI, MIYAKI, YUKIO, MIYASAKA, TSUTOMU, IDOTA, YOSHIO, C/O FUJI PHOTO FILM CO., LTD., KUBOTA, TADAHIKO, C/O FUJI PHOTO FILM CO., LTD., MISHIMA, MASAYUKI, C/O FUJI PHOTO FILM CO., LTD., MIYAKI, YUKIO, C/O FUJI PHOTO FILM CO., LTD., MIYASAKA, TSUTOMU, C/O FUJI PHOTO FILM CO., LTD.
Applicants: FUJI PHOTO FILM CO LTD, FUJI PHOTO FILM CO., LTD.
Application year: 1994
Main classification: H01M4
IPC codes: H01M4, H01M10